1. Field of the Invention
The present invention relates generally to scroll air compressors that compress air, and more particularly, to a water-injection type scroll air compressor that entrains water in air.
2. Description of the Related Art
In scroll air compressors, an orbiting scroll member with a nearly spiral wrap formed thereon is mechanically oscillated with respect to a fixed scroll member having a nearly spiral wrap formed thereon to mate with the wrap of the orbiting scroll member, and thus, air is compressed by the oscillation. Known examples of these scroll air compressors include an oil-cooled type that entrains an oil in air, and a water injection type that entrains water in air as described in JP-1996-128395-A (FIG. 10), for example. The oil or water entrained in air creates two actions. One seals the slight clearances between the wrap of the orbiting scroll member and that of the fixed scroll member, these wraps forming a plurality of compression chambers. The other suppresses the widening of the clearances by absorbing compression heat and preventing thermal deformation of members. These actions result in reduction in the amount of air leaking from each compression chamber, and hence, enhancement of compressor efficiency.
Because of their long history of field-proven application, scroll air compressors of the oil-cooled type are excellent in reliability. However, even if the oil included in the compressed air discharged from the compressor body is separated by an oil separator or the like, since the oil is likely to remain, albeit very small in quantity, in the compressed air, the oil-cooled type is unusable in applications that do not permit the presence of even a trace amount of oil, such as food or semiconductor processing. Scroll air compressors of the water-injection type, on the other hand, have been falling behind in proliferation, compared with the oil-cooled type, since the water-injection type requires preventive measures against rust, corrosion or insufficient lubrication, and the like, instead of involving no oil entrainment in compressed air. The market needs in recent years for oil-free clean air, however, are bringing about active development of water-injection type scroll air compressors.